1) Field of the Invention
The present invention relates to a sheet tension adjusting method and apparatus for, when guiding and conveying a single-faced corrugated fiberboard sheet or a liner through a roll for manufacturing a single-faced corrugated fiberboard in a manner of applying a paste onto peak portions of a corrugated sheet to adhere the liner thereto, adjusting the tension to be given to the single-faced corrugated fiberboard sheet or the liner.
2) Description of the Related Art
FIGS. 8 and 9 are illustrations each useful for describing a prior sheet tension adjusting means. FIG. 8 shows an arrangement for performing a tension adjustment for a single-faced corrugated fiberboard sheet S.sub.1 produced in a manner that a paste is applied onto the peak portions of a corrugated core paper (sheet) C.sub.1 and a liner L.sub.1 is adhered thereonto, while FIG. 9 illustrates an arrangement for conducting a tension adjustment for a liner L.sub.1 while conveying the liner L.sub.1 for manufacturing a single-faced corrugated fiberboard sheet S.sub.1.
In both the cases shown in FIGS. 8 and 9, a suction box 10 is placed in the vicinity of the single-faced corrugated fiberboard sheet S.sub.1 or the liner L.sub.1, and is communicated through a suction hose 11 to a suction pump 12 so that the air within the suction box 10 is sucked through the suction hose 11 when the suction pump 12 is put into operation.
With the above-mentioned constructions, for the tension adjustment of the single-faced corrugated fiberboard sheet S.sub.1, when the single-faced corrugated fiberboard sheet S.sub.1 comprising the corrugated core paper C.sub.1 and the liner L.sub.1 on conveyance passes in the vicinity of the suction box 10 as shown in FIG. 8, the single-faced corrugated fiberboard sheet S.sub.1 undergoes the suction from the liner L.sub.1 side by the suction box 10 to meet with a resistance, thereby changing and adjusting the tension to the single-faced corrugated fiberboard sheet S.sub.1.
Likewise, in the case of conducting the tension adjustment for the liner L.sub.1, when the liner L.sub.1 on conveyance passes in the vicinity of the suction box 10 as shown in FIG. 9, the suction box 10 sucks the liner L.sub.1 to make a resistance thereto, thus accomplishing the change and adjustment of the tension to the liner L.sub.1.
However, since these prior sheet tension adjusting means have a limitation in suction capacity of the suction box 10, the tension to the single-faced corrugated fiberboard sheet S.sub.1 or the liner L.sub.1 is changeable by only approximately 0.1 kgf/cm, and the expansion and contraction variation of the single-faced corrugated fiberboard sheet S.sub.1 or the liner L.sub.1 is as extremely small as approximately 0.01%. In addition, since the tension adjustment relies upon the frictional resistance force, i.e., depends upon the suction box 10 or the sheet surface conditions, the tension adjustment accuracy deteriorates.
For this reason, difficulty is encountered to adjust the upward warp or downward warp, thus impairing the quality of the corrugated fiberboard.